"""
*********
Shapefile
*********
Generates a networkx.DiGraph from point and line shapefiles.
"The Esri Shapefile or simply a shapefile is a popular geospatial vector
data format for geographic information systems software. It is developed
and regulated by Esri as a (mostly) open specification for data
interoperability among Esri and other software products."
See https://en.wikipedia.org/wiki/Shapefile for additional information.
"""
import networkx as nx
__all__ = ["read_shp", "write_shp"]
[docs]def read_shp(path, simplify=True, geom_attrs=True, strict=True):
"""Generates a networkx.DiGraph from shapefiles. Point geometries are
translated into nodes, lines into edges. Coordinate tuples are used as
keys. Attributes are preserved, line geometries are simplified into start
and end coordinates. Accepts a single shapefile or directory of many
shapefiles.
"The Esri Shapefile or simply a shapefile is a popular geospatial vector
data format for geographic information systems software [1]_."
Parameters
----------
path : file or string
File, directory, or filename to read.
simplify: bool
If True, simplify line geometries to start and end coordinates.
If False, and line feature geometry has multiple segments, the
non-geometric attributes for that feature will be repeated for each
edge comprising that feature.
geom_attrs: bool
If True, include the Wkb, Wkt and Json geometry attributes with
each edge.
NOTE: if these attributes are available, write_shp will use them
to write the geometry. If nodes store the underlying coordinates for
the edge geometry as well (as they do when they are read via
this method) and they change, your geomety will be out of sync.
strict: bool
If True, raise NetworkXError when feature geometry is missing or
GeometryType is not supported.
If False, silently ignore missing or unsupported geometry in features.
Returns
-------
G : NetworkX graph
Raises
------
ImportError
If ogr module is not available.
RuntimeError
If file cannot be open or read.
NetworkXError
If strict=True and feature is missing geometry or GeometryType is
not supported.
Examples
--------
>>> G = nx.read_shp("test.shp") # doctest: +SKIP
References
----------
.. [1] https://en.wikipedia.org/wiki/Shapefile
"""
try:
from osgeo import ogr
except ImportError as e:
raise ImportError("read_shp requires OGR: http://www.gdal.org/") from e
if not isinstance(path, str):
return
net = nx.DiGraph()
shp = ogr.Open(path)
if shp is None:
raise RuntimeError(f"Unable to open {path}")
for lyr in shp:
fields = [x.GetName() for x in lyr.schema]
for f in lyr:
g = f.geometry()
if g is None:
if strict:
raise nx.NetworkXError("Bad data: feature missing geometry")
else:
continue
flddata = [f.GetField(f.GetFieldIndex(x)) for x in fields]
attributes = dict(zip(fields, flddata))
attributes["ShpName"] = lyr.GetName()
# Note: Using layer level geometry type
if g.GetGeometryType() == ogr.wkbPoint:
net.add_node((g.GetPoint_2D(0)), **attributes)
elif g.GetGeometryType() in (ogr.wkbLineString, ogr.wkbMultiLineString):
for edge in edges_from_line(g, attributes, simplify, geom_attrs):
e1, e2, attr = edge
net.add_edge(e1, e2)
net[e1][e2].update(attr)
else:
if strict:
raise nx.NetworkXError(
"GeometryType {} not supported".format(g.GetGeometryType())
)
return net
def edges_from_line(geom, attrs, simplify=True, geom_attrs=True):
"""
Generate edges for each line in geom
Written as a helper for read_shp
Parameters
----------
geom: ogr line geometry
To be converted into an edge or edges
attrs: dict
Attributes to be associated with all geoms
simplify: bool
If True, simplify the line as in read_shp
geom_attrs: bool
If True, add geom attributes to edge as in read_shp
Returns
-------
edges: generator of edges
each edge is a tuple of form
(node1_coord, node2_coord, attribute_dict)
suitable for expanding into a networkx Graph add_edge call
"""
try:
from osgeo import ogr
except ImportError as e:
raise ImportError(
"edges_from_line requires OGR: " "http://www.gdal.org/"
) from e
if geom.GetGeometryType() == ogr.wkbLineString:
if simplify:
edge_attrs = attrs.copy()
last = geom.GetPointCount() - 1
if geom_attrs:
edge_attrs["Wkb"] = geom.ExportToWkb()
edge_attrs["Wkt"] = geom.ExportToWkt()
edge_attrs["Json"] = geom.ExportToJson()
yield (geom.GetPoint_2D(0), geom.GetPoint_2D(last), edge_attrs)
else:
for i in range(0, geom.GetPointCount() - 1):
pt1 = geom.GetPoint_2D(i)
pt2 = geom.GetPoint_2D(i + 1)
edge_attrs = attrs.copy()
if geom_attrs:
segment = ogr.Geometry(ogr.wkbLineString)
segment.AddPoint_2D(pt1[0], pt1[1])
segment.AddPoint_2D(pt2[0], pt2[1])
edge_attrs["Wkb"] = segment.ExportToWkb()
edge_attrs["Wkt"] = segment.ExportToWkt()
edge_attrs["Json"] = segment.ExportToJson()
del segment
yield (pt1, pt2, edge_attrs)
elif geom.GetGeometryType() == ogr.wkbMultiLineString:
for i in range(geom.GetGeometryCount()):
geom_i = geom.GetGeometryRef(i)
yield from edges_from_line(geom_i, attrs, simplify, geom_attrs)
[docs]def write_shp(G, outdir):
"""Writes a networkx.DiGraph to two shapefiles, edges and nodes.
Nodes and edges are expected to have a Well Known Binary (Wkb) or
Well Known Text (Wkt) key in order to generate geometries. Also
acceptable are nodes with a numeric tuple key (x,y).
"The Esri Shapefile or simply a shapefile is a popular geospatial vector
data format for geographic information systems software [1]_."
Parameters
----------
outdir : directory path
Output directory for the two shapefiles.
Returns
-------
None
Examples
--------
nx.write_shp(digraph, '/shapefiles') # doctest +SKIP
References
----------
.. [1] https://en.wikipedia.org/wiki/Shapefile
"""
try:
from osgeo import ogr
except ImportError as e:
raise ImportError("write_shp requires OGR: http://www.gdal.org/") from e
# easier to debug in python if ogr throws exceptions
ogr.UseExceptions()
def netgeometry(key, data):
if "Wkb" in data:
geom = ogr.CreateGeometryFromWkb(data["Wkb"])
elif "Wkt" in data:
geom = ogr.CreateGeometryFromWkt(data["Wkt"])
elif type(key[0]).__name__ == "tuple": # edge keys are packed tuples
geom = ogr.Geometry(ogr.wkbLineString)
_from, _to = key[0], key[1]
try:
geom.SetPoint(0, *_from)
geom.SetPoint(1, *_to)
except TypeError:
# assume user used tuple of int and choked ogr
_ffrom = [float(x) for x in _from]
_fto = [float(x) for x in _to]
geom.SetPoint(0, *_ffrom)
geom.SetPoint(1, *_fto)
else:
geom = ogr.Geometry(ogr.wkbPoint)
try:
geom.SetPoint(0, *key)
except TypeError:
# assume user used tuple of int and choked ogr
fkey = [float(x) for x in key]
geom.SetPoint(0, *fkey)
return geom
# Create_feature with new optional attributes arg (should be dict type)
def create_feature(geometry, lyr, attributes=None):
feature = ogr.Feature(lyr.GetLayerDefn())
feature.SetGeometry(g)
if attributes is not None:
# Loop through attributes, assigning data to each field
for field, data in attributes.items():
feature.SetField(field, data)
lyr.CreateFeature(feature)
feature.Destroy()
# Conversion dict between python and ogr types
OGRTypes = {int: ogr.OFTInteger, str: ogr.OFTString, float: ogr.OFTReal}
# Check/add fields from attribute data to Shapefile layers
def add_fields_to_layer(key, value, fields, layer):
# Field not in previous edges so add to dict
if type(value) in OGRTypes:
fields[key] = OGRTypes[type(value)]
else:
# Data type not supported, default to string (char 80)
fields[key] = ogr.OFTString
# Create the new field
newfield = ogr.FieldDefn(key, fields[key])
layer.CreateField(newfield)
drv = ogr.GetDriverByName("ESRI Shapefile")
shpdir = drv.CreateDataSource(outdir)
# delete pre-existing output first otherwise ogr chokes
try:
shpdir.DeleteLayer("nodes")
except:
pass
nodes = shpdir.CreateLayer("nodes", None, ogr.wkbPoint)
# Storage for node field names and their data types
node_fields = {}
def create_attributes(data, fields, layer):
attributes = {} # storage for attribute data (indexed by field names)
for key, value in data.items():
# Reject spatial data not required for attribute table
if key != "Json" and key != "Wkt" and key != "Wkb" and key != "ShpName":
# Check/add field and data type to fields dict
if key not in fields:
add_fields_to_layer(key, value, fields, layer)
# Store the data from new field to dict for CreateLayer()
attributes[key] = value
return attributes, layer
for n in G:
data = G.nodes[n]
g = netgeometry(n, data)
attributes, nodes = create_attributes(data, node_fields, nodes)
create_feature(g, nodes, attributes)
try:
shpdir.DeleteLayer("edges")
except:
pass
edges = shpdir.CreateLayer("edges", None, ogr.wkbLineString)
# New edge attribute write support merged into edge loop
edge_fields = {} # storage for field names and their data types
for e in G.edges(data=True):
data = G.get_edge_data(*e)
g = netgeometry(e, data)
attributes, edges = create_attributes(e[2], edge_fields, edges)
create_feature(g, edges, attributes)
nodes, edges = None, None